Ms Sarada,
While all cos do programming, they are not in the business of programming services.
Depending on the domain( manufacturing, Telecom..), service segment ( billing applications, sales application, plant maintenance..), Technology segemnt ( Mainframe, web based or web enabled etc..), Database orientation ( Oracle 10 g based or Access based...), Large clients ( not less than USD 500 million , or not more than Rs 500 cr) , domestic and overseas, direct contract or through Tier 1 or 2 vendor, and our keen ness to target low hanging fruits or high value fruits, we differe with each others.
With so large variables as business specialization, each co finds comfortable with margins available in their choice customer segment.
If the delivery calls for programmers DBAs, or architects, that does not make them to be in same business. Otherwise construction of a housing apartmnts, hotel, tower or dam will not be different. They call for specialised contractors who all use same masons, labourers, cement and building materials.
Each co depending on their owners. CEO or investor profiles ( tastes, comfort, aspirations, cambat guts, tenacity and passion to win) fall in their own area and segment of comfort or say incompetency. Recall Peter's principal-- everyone rises to the level of their incompetency. So are the IT orgns.
Can they not do more and differently. Certainly Yes, but are restricted by their management bandwidth and grasp of High and Low performance expectaions ( read sharing on the topic High and Low performance of individuals, teams and cos --in the same collectice X).
Trust now we agree all IT service cos are not doing same things.